Method for determining at least one parameter of two eyes by setting data rates and optical measuring device

ABSTRACT

The invention relates to a method for determining at least one parameter of two eyes ( 10   l ,  10   r ) of a test person ( 31 ), the method comprising the following steps:
         optically capturing of a first eye ( 10   l   ; 10   r ) of the two eyes ( 10   l   , 10   r ) by means of a first capturing unit ( 3   l   ; 3   r );   optically capturing the second eye ( 10   r;    10   l ) of the two eyes ( 10   l   , 10   r ) by means of a second capturing unit ( 3   r;    3 );   transmitting first signals concerning the captured first eye ( 10   l   ; 10   r ) from the first capturing unit ( 3   l   ; 3   r ) to an analysis unit ( 27 ) and transmitting second signals concerning the captured second eye ( 10   r;    10   l ) from the second capturing unit ( 3   r;    3   l ) to the analysis unit ( 27 );   determining the at least one parameter of the two eyes ( 10   l   , 10   r ) on the basis of the transmitted first and second signals in the analysis unit ( 27 ),   characterized by the following step:   setting a first data rate for the first signals and a second data rate for the second signals, wherein the first and the second data rate differ from each other, and wherein the transmitting of the first signals is effected at a first data rate and the transmitting of the second signals is effected at a second data rate.

The invention relates to a method for determining at least one parameterof two eyes of a test person, the method comprising the steps ofoptically capturing of a first eye of the two eyes by means of a firstcapturing unit, of optically capturing the second eye of the two eyes bymeans of a second capturing unit, of transmitting first signalsconcerning the captured first eye from the first capturing unit to ananalysis unit and transmitting second signals concerning the capturedsecond eye from the second capturing unit to the analysis unit, and ofdetermining the at least one parameter of the two eyes on the basis ofthe transmitted first and second signals in the analysis unit. Theinvention also relates to an optical measuring device for determining atleast one parameter of two eyes of a test person.

It is known from the prior art to use head mounted eye tracker devices.US RE39,539 E discloses an apparatus for monitoring movement of aperson's eye. The system includes a frame that is worn on a person'shead, an array of emitters on the frame for directing light towards theperson's eye, and an array of sensors on the frame for detecting lightfrom the array of emitters. The sensors detect light that is reflectedoff respective portions of the eye or its eyelid, thereby producingoutput signals indicating when the reflective portion of the eye iscovered by the eyelid. The system allows to monitor the persons level ofdrowsiness.

U.S. Pat. No. 6,163,281 discloses a system and method for communicationusing movement of a person's eye, including an emitter for directinglight towards an eye, a sensor for detecting emitted light from theemitter, and a processor coupled to the sensor for converting sequentiallight intensity signals received from the sensor to a stream of data,and/or for converting the signals into an understandable message.

US 2004/0196433 A1 discloses an eye tracking system for monitoring themovement of a user's eye comprising an eye camera and a scene camera forsupplying to interlace electronics video data indicative of an image ofthe user's eye and an image of the scene observed by the user. Inaddition, the system incorporates a frame grabber for digitizing thevideo data and for separating the eye and scene data into two processingchannels, and a spot location module for determining from the video datathe location of a reference spot formed on the user's eye byillumination of the user's eye by a point source of light. The systemfurther incorporates a pupil location module in order to determine theuser's line of gaze.

WO 2010/83853 A1 discloses a gaze point detection system with one ormore infrared signal sources to be placed in a test scene as referencepoints, at least one pair of eye glasses worn by a test subject, and adata processing and storage unit for calculating a gaze point of theperson. The eye glasses comprise an image sensor adapted to detect IRsignals from the at least one IR signal source and to generate an IRsignal source tracking signal, an eye tracking unit adapted to determinethe gaze direction of the test subject person and to generate an eyetracking signal, and a camera unit adapted to acquire a test scenepicture.

WO 2004/066097 A2 discloses an eye tracking system for displaying avideo screen pointer at a point of regard of a users gaze. The systemcomprises a camera focused on the user's eye, a support connected to thecamera for fixing the relative position of the camera to the user'spupil, and a computer having a CPU and an eye tracking interface. Bydetermining the center of the eye, a pointer on the video display screencan be displayed at the point of regard.

US 2010/0220291 A1 discloses an eye tracking system with a transparentlens, at least one light source, and a plurality of light detectors. Thetransparent lens is adapted for disposal adjacent an eye. At least onelight source is disposed within the transparent lens and is configuredto emit light towards the eye. The at least one light source istransparent to visible light. The plurality of light detectors isdisposed within the transparent lens and is configured to receive lightthat is emitted from the at least one light source and is reflected offthe eye. Each of the light detectors is transparent to visible light andis configured, upon receipt of light that is reflected off the eye, tosupply an output signal.

Known head mounted eye trackers suffer from the disadvantage that largedata quantities have to be processed in order to guarantee reliable eyetracking. Cameras monitoring the test person's eyes individually acquireand provide abundant data relating to characteristics concerning theeyes. This data needs to be transferred to an adequate processing unitquickly. Thus, significant bandwidth for the data transfer is required.Furthermore, the large data quantities have to get processed fast toachieve eye tracking in real time, i.e. with only little time delay.Consequently, expensive processing units are required, which suffer fromhigh power consumption, too. In particular, mobile and small eyetracking devices may thus get heavy, bulky and expensive. In addition toa head mounted unit an external device comprising a processing unit maybe necessary. State of the art devices, which are designed with leanercomponents, may suffer from not being able to keep pace with theabundant data stream. Loss of important data or significant time delayin the eye tracking functionality may be the result, thus compromisingreliable determination of parameters characterizing a captured eye.

An object of the present invention is to provide a method and an opticalmeasuring device which allow for a more reliable determination of atleast one parameter of two eyes of a test person.

This task according to the invention is solved by a method having thefeatures according to patent claim 1, and an optical measuring devicehaving the features according to patent claim 11. Advantageousembodiments of the invention are the subject-matter of the independentclaims and the description.

The method according to the invention serves for determining at leastone parameter of two eyes of a test person, the method comprising thefollowing steps:

-   -   optically capturing of a first eye of the two eyes by means of a        first capturing unit;    -   optically capturing the second eye of the two eyes by means of a        second capturing unit;    -   transmitting first signals concerning the captured first eye        from the first capturing unit to an analysis unit and        transmitting second signals concerning the captured second eye        from the second capturing unit to the analysis unit;    -   determining the at least one parameter of the two eyes on the        basis of the transmitted first and second signals in the        analysis unit; and    -   setting a first data rate for the first signals and a second        data rate for the second signals, wherein the first and the        second data rate differ from each other, and wherein the        transmitting of the first signals is effected at a first data        rate and the transmitting of the second signals is effected at a        second data rate.

As the first and second data rates differ from each other, one of thedata rates is smaller than the other one. Thus, the overall bandwidthrequired for transmitting the first and second data is reduced comparedto the state of the art. With the method it is, for example, possible tocapture a first parameter characterizing the first eye and a secondparameter, differing from the first parameter, characterizing the secondeye. Data relating to the first parameter are then transmitted with thefirst data rate, while data concerning the second parameter aretransmitted with the second data rate. Both parameters taken togetherthen allow reliable determination of one or more parameters of interestcharacterizing the two eyes. In particular, first and second parametersdo not need to be captured by both the first and second capturing unit.Capturing and transmission of redundant and superfluous information canbe avoided. This way, data streams can be kept lean. Despite reduceddata volume determining the at least one parameter of the two eyes canbe performed more reliably.

The capturing unit may comprise at least one camera. It is possible thatthe capturing of the respective eye with the first and second capturingunit is effected at the same data rate. The acquired data may then bepreprocessed such that data relating to the first capturing unit aretransmitted to the analysis unit with the first data rate while the datarelating to the second capturing unit are transmitted to the analysisunit with the differing second data rate. Alternatively, it may also bepossible that already data acquisition by the first and second capturingunits is effected at two differing data rates.

Advantageously, the method comprises the following steps:

-   -   providing data concerning the respective captured eye in the        first and/or the second capturing unit in dependency on the set        first or second data rate;    -   generating the first and/or second signals on the basis of the        provided data.        The capturing or acquisition data rate of the first and second        capturing units may thus differ. The first capturing unit may        optically capture the first eye according to the set first data        rate, while the second capturing unit may capture the second eye        with the second data rate. This way, already in the step of data        acquisition the amount of data is kept low. Only such data is        acquired which is indeed necessary to determine the at least one        parameter of the two eyes. Superfluous data are avoided right        from the start. The overall data volume is kept low.

Advantageously, in the step of providing the data a data compression independency of the set first or second data rate is performed. Inparticular, this step can be performed after data is acquired by thefirst and second capturing unit but before the respective data istransmitted to the analysis unit. The step may comprise preprocessing ofthe data. Known state of the art data compression algorithms may beused. Data compression may be different for data provided by the firstand second capturing units. For instance, data provided by the secondcapturing unit may undergo higher data compression than data provided bythe first capturing unit. Different data compression algorithms may beperformed in the first and second capturing units.

In one embodiment the method may comprise the following step: Setting atemporal capture resolution and/or a spatial capture resolution and/or acapturable image section, in particular a dynamic area of interest whichfollows the eye and can be adjusted with regard to its size and scanrate, of the first and/or the second capturing unit for the opticalcapturing of the respective eye in dependency on the set first or seconddata rate. In particular, a temporal capture resolution relates to atemporal data acquisition rate of the respective capturing unit. Forinstance, the first capturing unit may capture double the amount ofsignals during the same period of time as the second capturing unit. Thespatial capture resolution may be defined by a pixelated resolution. Ifthe spatial resolution of the first and second capturing unit is definedby the same pixel array with the same pixel size the spatial captureresolution of the first capturing unit may be four times as high as thespatial capture resolution of the second capturing unit if the secondcapturing unit performs a two-by-two binning. The capturable imagesection of the respective capturing unit may be a field of view of thiscapturing unit. This field of view may be dynamically adjusted to thegaze point of the respective captured eye. This way, first and seconddata acquisition rates can be flexibly adjusted. Depending on therespective situation an adequate first and/or second data rate can bechosen in an easy manner.

In one embodiment, the optical capturing of the first and second eye mayoccur with the same data rate but with a specific phase shift. While thefirst capturing unit is scanning the first eye, the second capturingunit may not scan the second eye and vice versa. The consecutivescanning intervals may be determined by a capturing rate, which may bethe same for both capturing units. However, a time delay betweenscanning intervals of the first and second capturing unit may beintroduced. If a parameter that is to be determined is virtually thesame, irrespective of whether the first or second eye is observed, thisredundancy together with the phase shift effectively results in anenhanced capturing rate. If, for example, the parameter that is to bedetermined is the pupil diameter, this diameter is usually the same forthe first and second eye. The first and second eye may then be capturedwith a capturing rate of 30 Hz each, the two capturing sequences beingshifted by half a period. The pupil diameter is then effectively sampledwith 60 Hz rate. Varying the phase shift is thus an elegant way to setthe desired data rate.

Advantageously, the method may comprise the following steps:

-   -   optically capturing a field of view, which at least partly        corresponds to a field of view capturable by the eyes of the        test person, by means of a third capturing unit;    -   transmitting third signals concerning the captured field of view        from the third capturing unit to the analysis unit; and    -   determining a correlation between the captured field of view and        the at least one determined parameter on the basis of the first        and third and/or second and third signals in the analysis unit.

In particular, the third capturing unit may be a scene camera. In apreferred embodiment depending on the first and third and/or second andthird signals the captured field of view can be switched from alandscape into a portrait mode or vice versa. Consequently, the field ofview captured by the third capturing unit may not be constant but may beadjusted depending, for example, on a point of regard of the two eyes,which may be determined on the basis of the first and third and/orsecond and third signals. Thus, only the field of view relevant in therespective situation is captured and unnecessary data is avoided. Inother embodiments the third capturing unit may comprise severalcapturing units or sensors, e.g. a scene camera and an infrared camera.

Advantageously, the method comprises the following step: determining athird data rate for the third signals, wherein the transmitting of thethird signals is effected at the third data rate, wherein the third datarate in particular is different from the first and/or second data rate.All three data rates may thus be chosen individually and in dependencyof the respective capturing situation. If, for example, a high firstdata rate is required, the second and/or third data rate can be adjustedaccordingly and respective lower values can be chosen for them.

In one embodiment the first data rate is set to be larger than thesecond data rate, and on the basis of the first and second signals adirectional view and/or a visual focus of the test person is determined.It may be possible that solely by optically capturing the first eye withthe first capturing unit a coarse direction of view and/or a coarsevisual focus may be determinable in the analysis unit. Then the dataacquired with the second capturing unit may allow a fine adjustment ofthe determined coarse direction of view and/or visual focus.Consequently, first and second data rates do not need to be equal butthe second data rate can be chosen to be lower than the first data rate.This way, the directional view and/or visual focus can be determinedvery precisely despite reduced overall data rates.

Advantageously, on the basis of the first and the second signals and/orthe first and the third signals and/or the second and the third signalsin the analysis unit a parallax correction is performed. One of thegroup of the first, second or third signals may then serve as a primarydata source for determining a point of regard. Another signal of thegroup of first, second and third signals may then serve as a correctivesignal to perform the parallax correction with respect to the point ofregard. Determining the point of regard may require a comparatively highamount of data and consequently a high data rate, while the datarequired for the parallax correction may be acquired and/or transmittedwith a comparatively lower data rate. The overall data rate is kept low.

Advantageously, the at least one captured parameter concerns anorientation and/or a position and/or an eyelid closure and/or a pupildiameter and/or a sclera characteristic and/or an iris characteristicand/or a characteristic of a blood vessel and/or a cornea characteristicof the at least one eye. In particular the at least one capturedparameter may concern a cornea radius (anterior, posterior), an eyeballradius, a distance pupil-center to cornea-center, a distancecornea-center to eyeball-center, a distance pupil-center to limbuscenter, a cornea keratometric index of refraction, a cornea index ofrefraction, a vitreous humor index of refraction, a distance crystallinelens to eyeball-center and to cornea center and to corneal apex, acrystalline lens index of refraction, a visual axis orientation, anoptical axis orientation, a pupil axis (achromatic axis) orientation, aline of sight orientation, an astigmatism degree (diopters) andorientation angle of flat and steep axis, an iris diameter, pupildiameters (pupil major and minor axes), pupil area), limbus major andminor axes, eye cyclo-torsion, eye intra-ocular distance, eye vergence,statistics over eye adduction/abduction and statistics over eyeelevation/depression. The optical measuring device can then work as aneye tracking device.

An optical measuring device according to the invention serves fordetermining at least one parameter of two eyes of a test person andcomprises a first capturing unit configured to optically capture a firsteye of the two eyes, a second capturing unit configured to opticallycapture the second eye of the two eyes, an analysis unit configured toreceive first signals concerning the captured first eye and transmittedby the first capturing unit and second signals concerning the capturedsecond eye and transmitted by the second capturing unit, and on thebasis of the transmitted first and second signals to determine the atleast one parameter of the two eyes, and an assigning unit configured toset a first data rate for the first signals and a different second datarate for the second signals, so that the transmission of the firstsignals to the analysis unit is effected at the first data rate and thetransmission of the second signals to the analysis unit is effected atthe second data rate.

In particular, the analysis unit and the assigning unit may be comprisedby a single processing unit and/or computer.

Advantageously, the optical measuring device may comprise a thirdcapturing unit configured to capture a field of view which at leastpartly corresponds to a field of view which is capturable by the eyes ofthe test person and configured to transmit third signals concerning thecaptured field of view at a third data rate to the analysis unit,wherein the assigning unit is configured to set the third data rate. Inparticular, the third capturing unit may be a camera. While the firstand second capturing units may be cameras observing the eyes of the testperson, the third capturing unit may be a scene camera capturing asimilar scene as seen by the test person. In particular, the first andsecond capturing units on the one hand and the third capturing unit onthe other hand may be directed into opposite directions.

Advantageously, the assigning unit may be configured to set the ratio ofthe first to the second data rate and/or the ratio of the first to thethird data rate and/or the ratio of the second to the third data rate tobe such that it assumes a value in the range of 1:5000 to 5000:1. Thewide range allows setting the respective data rates independently ofeach other. The overall data rate can be fine-tuned.

Advantageously, the assigning unit is configured to set the first and/orthe second and/or the third data rate in dependency on each other and/orin dependency on predeterminable parameters, in particular a datatransmission volume on a data line, and/or in dependency on apredeterminable measurement purpose of the optical measuring device.Consequently, one can make use of the full bandwidth provided by a dataline of the optical measuring device without leaving any bandwidthunused or surpassing the maximum data volume that can be transmitted.The respective data rates can dynamically adjust to the respectivesituation.

Preferentially, the optical measuring device comprises at least onecommon data line configured to transmit the first and second and/or thefirst and third and/or the second and third signals. The bandwidth of acommon data line is usually limited. By making the first, second andthird data rates adjustable, one can make use of the full bandwidthprovided. Compromising data by surpassing the allocatable bandwidth canbe prevented.

Advantageously, the first and/or the second and/or the third capturingunit comprise at least one camera.

Further features of the invention derive from the claims, the figures,and the description of the figures. All features and featurecombinations previously mentioned in the description as well as thefeatures and feature combinations mentioned further along in thedescription of the figures and/or shown solely in the figures are notonly usable in the combination indicated in each case, but also indifferent combinations or on their own.

The invention is now explained in more detail with reference toindividual preferred embodiments and with reference to the attacheddrawings. These show in:

FIG. 1A a front view of a spectacle device according to an embodiment ofthe invention;

FIG. 1B a side view of the spectacle device of FIG. 1A;

FIG. 1C a top view of the spectacle device of FIG. 1A;

FIG. 1D a perspective view of the spectacle device of FIG. 1A;

FIG. 2 a rear view of a spectacle device;

FIG. 3 a schematic rear view of a spectacle device with an eye cameramaking use of a deflection element to direct its optical path onto theeye;

FIG. 4 a side view of a spectacle device schematically showing theorientation of an eye camera;

FIG. 5 a schematic view of individual electronic components comprised bya spectacle device;

FIG. 6A a picture with a symbol indicating a large parallax errorattained with an optical measuring device according to the prior art;

FIG. 6B a picture showing a symbol indicating the lack of a parallaxerror with a spectacle device according to an embodiment of theinvention;

FIG. 7 a parallax error model;

FIG. 8 a diagram comparing parallax errors of measuring devicesaccording to the prior art and according to an embodiment of theinvention;

FIG. 9A a first field of view acquired by a scene camera;

FIG. 9B a second field of view acquired by the scene camera;

FIG. 10A a schematic side view of a spectacle device were the opticalpath of an eye camera extends in a straight line from the eye camera toan eye; and

FIG. 10B a schematic side view of a spectacle device where the opticalpath of an eye camera extends from the eye camera via a mirror to theeye.

In the figures same elements or elements of the same function areequipped with the same reference signs. FIGS. 2, 3, and 4 show the samereference frame with a Cartesian coordinate system and perpendicularaxes x, y and z.

FIGS. 1A to 1D show an optical measuring device which has the form of aspectacle device 1 or eye tracking device, respectively. The spectacledevice 1 is designed such that a person can wear it on its head justlike a normal pair of glasses. It comprises a frame 4 with two side bars5 l and 5 r which support the spectacle device 1 on the ears of theperson who is wearing it. Furthermore, the spectacle device 1 is held inplace on the head by a nose support 7. The mainframe has a specificwidth w1 and height h. Its length l depends on the length of thesidebars 5 l and 5 r. As can be seen in FIG. 1C the sidebars 5 l and 5 rare hinged to the front part of the frame 4 such that the distance w2between the side bars 5 l and 5 r can be enlarged or reduced (see dashedsidebar configuration for sidebar 5 l in FIG. 1C).

Alternatively, the optical measuring device may not be designed in formof a regular pair of eye glasses, but may be designed such that itresembles a helmet, forming a frame, with a face shield, forming a frameinsert.

Above the nose support 7 in the frame 4 a scene camera 2 is installed.It can either be attached to or integrated into the frame 4. With thescene camera 2 virtually a similar field of view can be captured as seenby a test person when wearing the spectacle device 1. In the lower partof the frame 4 the spectacle device 1 contains two eye cameras 3 l and 3r. When the spectacle device 1 is worn by a person the person's eyes canbe captured by the eye cameras 3 l and 3 r, which are integrated intothe frame 4 at a suitable angle. Eye cameras 3 l and 3 r are designed toobserve the person's left eye and right eye, respectively, i.e. capturecharacteristics of the person's eyes.

The frame 4 contains two openings which are filled with eye glass lenses8 l and 8 r thus forming frame inserts. The pictures acquired by thescene camera 2 and the eye cameras 3 l and 3 r lead to signals which areprocessed in one or several pre-processing units 6 integrated into thesidebars 5 l and 5 r.

FIG. 2 shows an inside view of the spectacle device 1. Along the rim ofthe frame part enclosing the eye glass lenses 8 l and 8 r several LightEmitting Diods (LEDs) 9 are located in a ring arrangement. When thespectacle device 1 is worn by a person, those LEDs 9 can illuminate theeyes of the test person in a defined way. The LEDs 9 will causereflections on the eyes of the test person (cornea reflections) for allpossible gaze angles. Those reflections can be detected by the eyecameras 3 l and 3 r and can be used for eye tracking.

The LEDs 9 can be switched on an off individually, in groups or alltogether following a specific time pattern, strobe characteristic orspatial variation. The on-off-switching-frequency of different LEDs 9 orgroups of LEDs 9 may vary. Certain groups of LEDs 9 may get switched onexactly when other groups of LEDs 9 get switched off. A specific spatialand temporal correlation pattern may be implemented with regard to theswitching and thus illumination characteristics. This way a reflectionpattern can be created on the eyes that can be recognized easily by theeye cameras 3.

The overall setup with the most important electronic components is shownin FIG. 5. The eye cameras 3 l and 3 r are connected to specific cameraelectronics 15 by 100 mm long cables 14. In particular, the cameras 3 land 3 r comprise only basic electronic components while their majorelectronic components are located within the camera electronics 15. Thisway, the primarily “optical part” of the cameras 3 l and 3 r can belocated remote to the primarily “electronic part” within the cameraelectronics 15. Both parts can then be connected by flex-PCB cables 14.This way, the optical sensor and the basic electronic components withinthe cameras 3 l and 3 r form a very small and highly compact entitywhile bulkier electronic components within the electronics 15 can beplaced on more spacious integrated circuit boards elsewhere. Theelectronics 15 are connected to a pre-processing unit 16 which canprocess the signals from the eye cameras 3 l and 3 r. The pre-processingunit 16 can be identical to the pre-processing unit 6 located in thesidebars 5 l and 5 r of the spectacle device 1. The pre-processing unit16 is connected to a USB-hub 19. The LEDs 9 installed in the frame 4form a first and a second IR LED chain 21 and 22 arranged in a ringconfiguration around the eye glass lenses 8 l and 8 r. The IR LED chains21 and 22 are connected to an IR LED constant current source 20, whichis also connected to the USB-hub 19. The USB-hub 19 additionally servesas a power source for the IR LED constant current source 20. The LEDs 9of the IR LED chains 21 and 22 can be switched on an off individually.To achieve this, they may be connected to the IR LED constant currentsource 20 in a parallel network with individual electrical switches foreach LED 9 being implemented.

The USB-hub 19 is connected via a serial interface or USB cable 25 to apre-processing unit 26. The signals pre-processed in the pre-processingunit 26 are finally analyzed in a personal computer 27, which contains arecorder device 28. An additional aux-/sync-port 13 forming an interfaceon the spectacle device 1 can also be connected to the USB-hub 19. Theaux-/sync-port 13 can serve as interface for synchronization with otherelectronic devices or for triggering parallel data acquisitions. Theelectronics 15, pre-processing unit 16, USB-hub 19 and IR LED constantcurrent source 20 are located on a common printed circuit board PCB 23.

In analogy to this setup the scene camera 2 is also connected toelectronics 15 via a 100 mm cable 14. In this case the electronics 15are located on a second printed circuit board PCB 24, which alsocontains a pre-processing unit 17. The pre-processing unit 17 can bebased on electronics according to the DaVinci digital signal processor(DSP). It contains an MPEG encoder 18 for encoding the signals receivedfrom the electronics 15. A microphone 12 may also be connected to thepre-processing unit 17. The pre-processing unit 17 located on the PCB 24is connected to the USB-hub 19. This way, processing signals acquired bythe scene camera 2 are finally analyzed in the personal computer 27.

The pre-processing units 6, 16, 17 and 26 may be able to compress atleast one of the three image streams generated by the two eye cameras 3l and 3 r and the scene camera 2. Here, different alternatives arepossible. A pre-processing unit may compress only the image stream ofone camera while each camera has its own pre-processing unit.Alternatively, a single pre-processing unit may compress the imagestreams of all cameras. Furthermore, the pre-processing units may beconfigurable via a system interface and corresponding software to managethe bandwidth by adjustment of resolution, region of interest, framerate and compression parameters. The pre-processing units may bedesigned to trigger synchronously the camera's image acquisition. Theymay provide time stamps for each acquired image which can be used tosynchronise several or all camera data streams offline.

The pre-processing units may either be located on integrated circuitboards of the cameras or on a separate integrated circuit board that islocated at or on a head mount (e.g. in the side bar 5 l or 5 r of thespectacle device 1) or in a separate housing that is worn by the testperson 31, e.g. on a belt.

The spectacle device 1 may also comprise an auxiliary interface whichallows to acquire data in real time from external sensors. Such sensorsmay be biometric sensors (including but not limited to EEG, ECG, etc.)or attitude sensors (including but not limited to accelerometers,magnetometers, gyroscopes, etc.). It is then possible to synchronise thedata stream of the external sensors with the data streams acquired fromthe cameras 2, 3 l and 3 r. Furthermore, an external clock or triggersignal can be provided that can be used by the external sensors tosynchronise themselves with the system. The bandwidth of data acquiredfrom the interface can be reduced or compressed by means of on-boardprocessing resources integrated in the system in its dedicated recordingunit 28.

The eye cameras 3 l and 3 r can either be suited for visible or nearinfrared light. They are located symmetrically with respect to avertical centre line that divides the user's face into two halves. Theeye cameras 3 l and 3 r may be positioned in front and below the eyes 10l and 10 r respectively, for example in or at the lower rim of a pair ofeye glass lenses 8 l and 8 r, pointing at the eyes 10 l and 10 r in anangle of 30° to 50° and being mounted in the frame 4 in an angle a of30° to 50°. In the embodiment the eye cameras 3 l and 3 r are sensitivein the near infrared.

In the embodiment the eye cameras 3 l and 3 r are sensitive in the nearinfrared. They have a resolution of 640*480 and are read out with a 60Hz frequency.

The scene camera 2 can be located on a vertical centre line that dividesthe user's face into two halves in or at the nose bridge of the frame 4.Alternatively, it may also be located at, in or close to the rim of ahelmet, cap or headband. The scene camera 2 may have HD (highdefinition) and/or adjustable resolution. It can either be mounted inlandscape or portrait orientation. Furthermore, it can be mounted suchthat its orientation can be changed from landscape to portraitorientation (camera roll) and also the direction the camera is pointingin (camera pan and tilt).

Instead of a single scene camera 2, the spectacle device 1 can alsocomprise a pair of scene cameras, where each scene camera can beoriented either in portrait mode or in landscape mode. Furthermore, eachscene camera can be oriented independently of the respective secondscene camera. Alternatively, both scene cameras 2 may have fixedorientations, which may or may not differ from each other.

Furthermore a prism or lens can be mounted in front of the scene camera2 to create a different positioning of the field of view of the scenecamera 2 with respect to the glasses, especially a more downwardoriented field of view for near range reading applications.

Six LEDs 9 are located around each eyeglass lens 8. They emit in theinfrared wavelength range (typically above 750 nm and below 1000 nm) ata central wavelength of 850 nm. They are driven by 50 mA currentprovided by the IR LED constant current source 20.

Instead of direct illumination of the eyes with the LEDs 9 also animplementation with a light guide can be envisaged. One or severalsegments of light guides (e.g. fiber optics) may be used. Theillumination of the eyes may be implemented with focusing optics(structured illumination). Instead of the LEDs 9 suitable diffractiveoptics or lasers may be used to generate a pattern of coherent light forilluminating the eyes. The light source can be used together with anoptical element in order to create a pattern of reflections on the eyes10 l and 10 r (e.g. with focusing optics or diffractive optics). Theillumination source may either emit visible or near infrared light. Theillumination source may be positioned in or on the frame 4, inparticular in a circle-like arrangement around the eye glass lenses 8 land 8 r. Alternatively, the illumination source may be located on therim or frame of a head mounted display. It may specifically be designedto create a pattern of reflections on the eye surfaces of the testperson 31.

When the spectacle device 1 shown in FIG. 2 is worn by a test person thesituation shown in FIG. 10A in a simplified way is realized. The eyecamera 3 is arranged in such a way on the frame 4 that with thespectacle device 1 fixed to the head of a test person the optical path Mcapturing at least one parameter of the eye 10 extends in a straightline from the eye camera 3 to the eye 10.

FIGS. 3 and 10B show a different configuration of the spectacle device1. The spectacle device 1 comprises a mirror 11, forming an opticaldeflection element attached to the frame 4, the mirror 11 and the eyecamera 3 being arranged in such a way on the frame 4 that with thespectacle device 1 fixed to the head of the test person the optical pathM for capturing at least one parameter of the eye 10 extends from theeye camera 3 via the mirror 11 to the eye 10. The three dimensionalrepresentation of FIG. 3 shows the spectacle device 1 from a rear orinside view. In the figure, reflections of the left and right eye 10 land 10 r, respectively, show in the eyeglass lenses 8 l and 8 r. Thecoordinate system is a Cartesian one with the z-axis being directed intothe plane of projection.

Thus, the eye cameras 3 l and 3 r may be mounted in front of and abovethe eyes 10 l and 10 r with an optical guide or mirror 11 located infront and below the eyes 10 l and 10 r, for example in or at the lowerrim of a pair of eye glass lenses 8 l and 8 r in order to acquire animage of each eye 10 l and 10 r from a forward and low perspective andto make that image visible to the eye cameras 10 l and 10 r. The opticalguide or mirror 11 can either be a (flat) mirror, a spherical mirror, adome, a custom lens, a holographic image guide, etc. The mirror 11 canbe reflecting only a specific range of wavelength and be transparent toothers.

The mirror 11 can either be a flat mirror or a spherical mirror. Theadvantage of a spherical mirror is that it magnifies the field of viewof the eye camera 3 beyond the field of view achievable with a flatmirror. The configuration of FIG. 3 furthermore allows to place theoptical system very close to the eye 10 (set direction) thus improvingergonomics and aesthetics. The test person's own field of view is hardlyobstructed. The mirror 11 can be a so-called hot mirror, i.e. the mirror11 is transparent in the visible wavelength range while having a higherreflectivity in the infrared wavelength range. It can be very thin andhollow (so-called dome) thus, minimizing the distortion due torefraction. It can be made out of a material showing a very low index ofrefraction (IOR).

In both cases (FIGS. 10A and 10B) the eye camera 3 is arranged in such away that the optical path M for the capturing of at least one parameterof the eye 10 excludes the frame insert, i.e., the eye glass lens 8.Furthermore, the eye glass lens 8 is arranged in such a way that theoptical axis K of the eye 10 and the optical path M as single jointlyused optical element comprise the eye 10. Furthermore, the optical pathM entirely runs within a space Sp which extends on the side of the eyeglass lens 8 facing the eye 10.

The embodiments shown in FIGS. 2 and 3 and FIGS. 10A and 10B,respectively, both reduce eye occlusion due to the upper eye-lid.

FIGS. 6A to 8 illustrate the reduction of parallax errors in thespectacle device 1 compared to the prior art. As can be seen in FIG. 6Athe position of an object 29 the test person actually focuses its eyeson and the point of regard 32 determined by the spectacle device 1usually do not coincide very well when using spectacle devices 1 asknown from the prior art. This effect is usually the more pronounced thecloser the test person is located to the object 29 that is to befocused. However, with the spectacle device 1 according to an embodimentof the invention the coincidence between the determined point of regard32 and the actual object 29 is very good, even for measuring distancesas low as 0.5 m (see FIG. 6B). This is achieved by minimizing thedistance between the eye ball center and the camera focal point.

The situation is again illustrated in FIG. 7. As eye 10 and scene camera2 are located at slightly different positions the difference in theirrespective viewing angles for focussing the object 29 becomes the morepronounced the closer the object 29 is located to the eye 10 and scenecamera 2, respectively (i.e. larger distortions for smaller z-values).The spectacle device 1 may get calibrated in the situation shown in FIG.6B. The object 29 then lies in the calibration plain P and bycalibrating the spectacle device 1 one can make sure that the determinedpoint of regard 32 indeed falls onto the actual object 29. Calibrationis typically performed on a plane at some distance from the testsubject. It relates measured gaze direction (angles) to pixels in thescene video frame. This calculation gives valid results only for pointsthat lie in that calibration plane. For points that do not lie on thatplane, a systematic error (parallax) is introduced. When the distance ofthe spectacle device from the object 29 is increased the differencebetween the distance to the calibration plain P and the actual distanceto the object 29 causes the pronounced deviations. With the spectacledevice 1 according to an embodiment of the invention these deviations orparallax errors (indicated by symbols S2, circles, in FIG. 8) for alldistances d are considerably smaller than with devices according to theprior art (symbols S1, rectangles). Thin-lined crosses relate to thegroup of symbols S2, while bold crosses relate to the group of symbolsS1. The crosses correspond to the point of regard 32 used forcalibration purposes.

The parallax error is mathematically modelled as a function of theposition of the scene camera 2 with respect to the eye position. Thegaze estimation error due to parallax is minimized by placing the scenecamera 2 as close as possible to the eye 10, according to the resultsshown by the mathematical simulation. The parallax error can be furthercorrected by estimating the distance to the point of regard by usingvergence from binocular tracking and by estimating the position of theeyes with respect to the eye tracking device.

To achieve even better results the field of view of the scene camera 2can be optimized. The scene camera 2 with standard optics has a field ofview that does not cover the full physiological gaze range (horizontalfield of view of standard optics: 40° to 50°; typical physiological gazerange:)60°. In an embodiment the field of view of the scene camera 2 canthus be optimized depending on the respective application. One suchfield of view optimization method is illustrated in FIG. 9A and 9B. Auser wearing the spectacle device 1 is at the same time observing abackground B and his mobile phone 30. According to FIG. 9A the field ofview FOV1 mainly covers the background B. When the test person 31 looksdown onto its mobile phone 30 the change in gaze direction isautomatically determined by the eye cameras 3 l and 3 r and the scenecamera's 2 field of view is automatically adjusted by switching fromlandscape to portrait orientation (field of view FOV2). This can beachieved by a z-axis 90° mechanical roll of the scene camera 2 or by theuse of an optical prism in front of the scene camera 2. Also the use oftwo scene cameras with different tilt or roll angles is possible.Alternatively, also an optical beam splitter may be used in front of thescene camera 2.

In summary, the spectacle device 1 forms a head-mounted eye trackingsystem which consists of three cameras: two eye cameras 3 l and 3 r andat least one scene camera 2. The three cameras 3 l, 3 r and 2 can have amanageable bandwidth, for example by adjustable frame rates orresolutions. One or several pre-processing units 6, 16, 17 and 26 mayexist that perform variable compression of the video streams receivedfrom the cameras 2, 3 l and 3 r. The level of compression of the videostreams may be the same for the eye cameras 3 l and 3 r and the scenecamera 2, or the video streams may be separately compressed for the eyecameras 3 l and 3 r and the scene camera 2. The frame rate for eyecamera 3 l may correspond to full speed acquisition, the one of eyecamera 3 r may correspond to 1/10 speed acquisition and the one for thescene camera 2 may correspond to ½ speed acquisition. Instead ofadjusting the frame rates of the different cameras, alternatively theacquisition rates may be chosen to be the same, while data processing isperformed differently for each camera. Data provided by one camera maybe compressed more than data provided by another camera, although bothcameras acquire the same amount of data. One may also combine differentcompression rates with different acquisition rates. It is also possibleto omit, for example, every second acquired image when transferring thedata and thus reduce the amount of data to be sent to the CPU by half.The signals of the cameras 2, 3 l and 3 r may be transferred to a CPU inthe PC 27 via a wired or wireless interface (see FIG. 5). Auxiliaryinterfaces for other data sources and methods for synchronisation withthese data sources may be implemented in the spectacle device 1.

The spectacle device 1 can come as a system comprising severalexchangeable pieces. The spectacle device 1 can have an exchangeable setof nose pieces or nose supports 7 for faces with small or large noses.This way, the spectacle device 1 can be worn over vision correctionglasses without a problem. Furthermore, the spectacle device 1 has aholding mechanism for exchangeable glasses that can have differentlevels of light transmittance (e g. clear glasses or sun glasses) for acertain range of wavelengths. Additionally or alternatively theexchangeable glasses can have a near infrared optical filter to matchthe wavelength of the illumination source and block some or all lightfrom the outside of same and similar wavelengths from reaching the eyesurface to improve signal to noise on the eye surface. The spectacledevice 1 has rims and a nose bridge that serve as a mount or housing forthe eye cameras 3 l and 3 r and the scene camera 2. The eye cameras 3 land 3 r are mounted in such a way that their field of view extendsbehind the exchangeable glasses 8 l and 8 r.

With the spectacle device 1 it is possible to do eye tracking,occulometrics, biometrics and position and motion measurements in orderto measure and classify as fully as possible human behaviour in a freerange movement setup. A head mounted eye tracking device is realisedwhich is calibration-free and provides an astigmatism estimation. Theeye-tracking functionality has zero set-up time. No adjustments arenecessary. A test person 31 can just put the spectacle device 1 on andstart using it. It has a very large gaze-tracking range covering thephysiological range of human eye movement (80° horizontal, 60°vertical). It is very robust and has a high accuracy in gaze mapping.Astigmatism is compensated for, parallax is minimized, pupil axis shiftis compensated and the device is calibration free or can be calibratedusing a one-point calibration feature. Furthermore, it is designed towork irrespective of ethnic group (Caucasian, Asian, African, etc.),gender and age. The field of view of the scene camera 2 is optimized. Bythe use of optical, inertial or magnetic sensors a head trackingfunctionality can be implemented. The spectacle device furthermoreoffers biometric features, such as measuring the pupil diameter andoffering interfacing and synchronisation options with EEG, ECG, etc.Finally, it can be integrated with a head mounted display. It ispossible to project a virtual image onto a subject's eye of a portablecomputer screen. Furthermore, the possibility is offered to interactwith “objects” in the virtual image using eye movement (gaze, blinks).

Head tracking functionality can be realized by the use of three axisgyroscopes, three axis accelerometers and/or three axis magnetometerswith optional sensor fusion for six dimensional head tracking.

In summary, the spectacle device 1 offers a very specific optical andelectronic architecture. With respect to the electronic architecturethree or more high resolution cameras with allocateable bandwidth areincorporated in the device 1. Separate processing channels for eyecameras 3 l and 3 r and the scene camera 2 are envisaged. The opticalarchitecture is characterized by exchangeable glasses with variousproperties. The optical path of the eye cameras 3 l and 3 r extendsbehind the glasses or eye glass lenses 8 l and 8 r respectively.Furthermore, a set of LEDs 9 allows for highly variable illumination ofthe eyes 10 l and 10 r. For instance, the illumination geometry aroundthe eye can be controlled. The specific LED subsets can be controlledwith regard to strobe effect and sequencing. Finally, eye illuminationcan be achieved by point, line or two-dimensional light sources.

REFERENCE SIGNS

1 spectacle device

2 scene camera

3, 3 l, 3 r eye camera

4 frame

5 l, 5 r side bar

6 pre-processing unit

7 nose support

8, 8 l, 8 r eyeglass lens

9 LED

10, 10 l, 10 r eye

11 mirror

12 microphone

13 aux-/sync-port

14 cable

15 electronics

16 pre-processing unit

17 pre-processing unit

18 MPEG encoder

19 USB hub

20 IR LED constant current source

21, 22 IR LED chain

23, 24 PCB

25 USB 2.0 cable

26 pre-processing unit

27 PC

28 recorder

29 object

30 mobile phone

31 test person

32 point of regard

w1, w2 width

h h height

l length

a tilt angle

K optical axis

M optical path

O origin of system of reference

P calibration plane

Sp space

d distance

S1, S2 symbols

B background

FOV1, FOV2 field of view

x, y, z axis

1. A method for determining at least one parameter of two eyes of a testperson, the method comprising: optically capturing of a first eye of thetwo eyes by means of a first capturing unit; optically capturing thesecond eye of the two eyes by means of a second capturing unit;transmitting first signals concerning the captured first eye from thefirst capturing unit to an analysis unit and transmitting second signalsconcerning the captured second eye from the second capturing unit to theanalysis unit; determining the at least one parameter of the two eyes onthe basis of the transmitted first and second signals in the analysisunit, characterized by the following step: setting a first data rate forthe first signals and a second data rate for the second signals, whereinthe first and the second data rate differ from each other, and whereinthe transmitting of the first signals is effected at a first data rateand the transmitting of the second signals is effected at a second datarate.
 2. The method according to claim 1, characterized by thefollowing: providing data concerning the respective captured eye in thefirst and/or the second capturing unit in dependency on the set first orsecond data rate; generating the first and/or second signals on thebasis of the provided data.
 3. The method according to claim 2,characterized in that in the step of providing the data a datacompression in dependency of the set first or second data rate isperformed.
 4. The method according to claim 1, characterized by thefollowing: setting a temporal capture resolution and/or a spatialcapture resolution and/or a capturable image section, in particular adynamic area of interest, which follows the eye and can be adjusted withregard to its size and scan rate, of the first and/or the secondcapturing unit for the optical capturing of the respective eye independency on the set first or second data rate.
 5. The method accordingto claim 1, characterized by the following: optically capturing a fieldof view, which at least partly corresponds to a field of view capturableby the eyes of the test person by means of a third capturing unit;transmitting third signals concerning the captured field of view fromthe third capturing unit to the analysis unit; determining a correlationbetween the captured field of view and the at least one determinedparameter on the basis of the first and third and/or second and thirdsignals in the analysis unit.
 6. The method according to claim 5,characterized by the following: determining a third data rate for thethird signals, wherein the transmitting of the third signals is effectedat the third data rate, wherein the third data rate in particular isdifferent from the first and/or second data rate.
 7. The methodaccording to claim 5, characterized in that the first data rate is setto be larger than the second data rate, and on the basis of the firstand second signals a direction of view and/or a visual focus of the testperson is determined.
 8. The method according to claim 1, characterizedin that on the basis of the first and the second signals and/or thefirst and the third signals and/or the second and the third signals inthe analysis unit a parallax correction is performed.
 9. The methodaccording to claim 1, characterized in that the transmitting of thefirst and/or second and/or third signals is effected via a common dataline.
 10. The method according to claim 1, characterized in that the atleast one captured parameter concerns an orientation and/or a positionand/or an eyelid closure and/or a pupil diameter and/or a scleracharacteristic and/or an iris characteristic and/or a characteristic ofa blood vessel and/or a cornea characteristic of the at least one eye.11. An optical measuring device for determining at least one parameterof two eyes of a test person, the optical measuring device comprising: afirst capturing unit configured to optically capture a first eye of thetwo eyes; a second capturing unit configured to optically capture thesecond eye of the two eyes; an analysis unit configured to receive firstsignals concerning the captured first eye and transmitted by the firstcapturing unit and second signals concerning the captured second eye andtransmitted by the second capturing unit, and on the basis of thetransmitted first and second signals to determine the at least oneparameter of the two eyes, characterized by an assigning unit configuredto set a first data rate for the first signals and a different seconddata rate for the second signals, so that the transmission of the firstsignals to the analysis unit is effected at the first data rate and thetransmission of the second signals to the analysis unit is effected atthe second data rate.
 12. The optical measuring device according toclaim 11, characterized by a third capturing unit configured to capturea field of view which at least partly corresponds to a field of viewwhich is capturable by the eyes of the test person, and configured totransmit third signals concerning the captured field of view at a thirddata rate to the analysis unit, wherein the assigning unit is configuredto set the third data rate.
 13. The optical measuring device accordingto claim 11, characterized in that the assigning unit is configured toset the ratio of the first to the second data rate and/or the ratio ofthe first to the third data rate and/or the ratio of the second to thethird data rate to be such that it assumes a value in the range of1/5000 to 5000/1.
 14. The optical measuring device according to claim11, characterized in that the assigning unit is configured to set thefirst and/or the second and/or the third data rate in dependency on eachother and/or in dependency on pre-determinable parameters, in particulara data transmission volume on a data line, and/or in dependency on apre-determinable measurement purpose of the optical measuring device.15. The optical measuring device (1) according to claim 11,characterized by at least one common data line configured to transmitthe first and second and/or the first and third and/or the second andthird signals.